Rheostat.



no. 689,445. Patented na. 24, rem.

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RHESTAT.

. (Application led Oc't. 13, 1900A (No Model.) l 2 Sheets-Sheet l.

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Nn. 689,445. Patented nec. 24, mol.

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' RHEOSTAT.

f (Application med ou'. 1s, 1900.)

v (No Model.)

g sheets-snm 2.

. fo all whom it may concern.-

`* UNITED STATES PATENT OFFICE.

CHARLES WIRT, OF PHILADELPHIA, PENNSYLVANIA.v

RH EOSTAT.

SPECIFICATION :formingl part f Letters Patent NIO. 689,445, dated December 24, 1901.

Application iiled October 13,1900. Serial No. 32,948. (No model.)

Be it known that I, CHARLES WIRT, a citizen of the United States, residing in Philadelphia, in the county of Philadelphia and Stateof Pennsylvania, have invented a certainnew and useful Improvement in Rheostats, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

" My invention relates to a rheostat, my ob- Y ject being to provide an improvement upon the general form Vof rheostat illustrated in Letters Patent No. 633,172, granted to me September 19, 1899. In said patent above referred to I have shown a rheostat in which the resistance-conductor is formed from` a ribbon of German silver or similar material formed into a plurality' of resistancesections or coils, which in practice are-adapted to occupy radial positions and-= to rest'in contact with contact-bars with which the contact element of the rhoestat is adapted to engage, these several par-ts being clamped 4between suitable casing-plates. In said application I have shown the resistance-ribbon formed of uniform width throughout and have also shown the contact-bars with which the ribbon makes electrical contact also formed of uniform Width.

In accordance with the present invention I form the resistance-ribbon of continuouslydecreasing Width, from oneend'to the otherthat is, tapered-so that by making the resistance-sections of the same number of turns or convolutions throughout a 'resistance-conductor is provided in which the resistancesections are of continuously and uniformly increasing resistance from onel end of the rheostat tofthe other. I preferably connect this resistance-conductor in circuit, so that when but a smallportion of the rheostat-resistance is included incircuit the resistances'ections of large cross-section will be in service, while themovem'ent of the rheostat-arm to include more vresistance in circuit serves to cut into thefcircuit the resistance-sections of decreased crossesection. Bythis arrange- "ment the crosslsection of the conductor in circ-uitvaries indirect proportion to the current flowing-that is, when the rheostat-resistance is small and a relatively large cur# rent is flowing the cross-sectionof the resistance-sections in circuit is large, While when a larger resistance is included in circuit the sections ofless cross-section arc traversedby current; but due to the increased resistancein circuit, the current o'wing is relatively smaller. The resistance-ribbon of continuously-decreasing width thus permits the construction of a rheostat which is more efficient and which more readily accomm'ol` dates itself tothe varying conditions of use than would be the case'were theY ribbonof uniform cross section. rangement permitsa vmore uniform distribui' Moreover, this ar tionof heat during theoperation of the rheo` stat.' Q Since the widths ofthe contact-bars with which the resistance-sections engage vary'fromv one end of the rheostatto the other, the contact-surface between -the resistance-section and the contact-bar varies in accordance with the requirement for carrying capacity. Thus for wide'resistance-sections which are calledupon tok carry large currents the contact-surface between the ribbon and the'contact-bar is relatively large, while the surface-contact between narrower resistance-sections and the corresponding contactbars is smaller to xaccommodate the lesser maximum current which flows through these sections of decreased Width. `Again,`tlie contact-bars of varying Widths facilitate the conduction of the current from the contact-bars to the 'movable contact-arm of the rheostat by varyingy the surface contact between theI contact-bars and the contact-arm in accordancewith the strength of the current flowingthat is,when small resistance is included in circuit and alan-ge current is iiowing the contact-arm rests upon one of-fthe widecontact-bars,while when a greater resistance is'ineluded in circuit the contact-arm res-ts upon a narrower'bar. By thusformingtheresistanceribbon with continuously-decreasing width from one end to the other and by theemployment of contact-bars of varying widths, as above described, I am able to produce a rheostat which possesses many points of advantage over rheostats of the prior art.

lNIy invention also contemplates various de'- tails of mechanical construction,which will be IOO hereinafter more particularly described and claimed.

I have illustrated my invention in the accompanying drawings, in Which- Figure l is a plan view of the rheostat of my invention, showing a portion of the top plate and insulation broken away. Fig. 2 is a sectional View on line 2 2, Fig. l. Fig. 3 is a partial bottom view of the rheostat, showing one of the casing-plates removed. Fig. 4 is a View illustrating` the manner of mounting the clamping-strip upon the contact-bar. Fig. 5 is a view illustrating the resistance-section in position upon the contact-bar. Fig. 5a is a View of a modification of the contact-bar. Fig. 6 is a detail view showing the manner of securing the casing-plates together at the edges. Fig. 7 is a sectional view ou line 7 7, Fig. 3.

Like letters refer to like parts in the several figures.

Upon the inner face of the casing-plate ct an annular ring b, of asbestos or similar insulating material, is placed, and a similar annular ring b', ofinsulating material, is mounted upon the inner face of the opposite casingplate ce. The resistance-conductor is interposed between the two layers of insulating material and is clamped between the casingplates a ct. This resistance-conductor consists of a thin ribbon c, of resistance material, such as German silver, and the ribbon is Wound to form a plurality of resistance-sections c c', adapted in the complete rheostat to occupy positions side by side, as illustrated. These several resistance-sections are formed from a continuous and integral ribbon, and this ribbon is of continuously decreasing width from one end to t-he other, the ribbon being thus formed with a taper. The result ot' this construction is that the `cross-section and consequently the carrying capacity of the conductor vary from one end tothe other. The several resistance-sections c c are adapted to rest upon and to make electrical contact with contact-bars ol d, which in the specific embodiment illustrated occupy radial positions and which are of successively-decreasing width from one end of the rheostat to the otherthat is, each coutact-bar is of less width than its neighbor or the bars of a group are-ot' less Width than the bars of an adjacent group. The inner ends of these contact-bars project beyond the edge of the annular casing-plate a to form the rheostat-terminals, with which the movable element or contact-arm of the rheostat is adapted to engage.

While I have illustrated a rheostat of the circular form, it will be understood that my invention is equally applicable to a rheostat in which the contact-terminals are not arranged in a curve.

I have illustrated in Figs. t and the construction which I preferably employ for mounting the resistance-sections upon the contact-bars. Upon the face of contact-bar d a strip d of tin or other material is mounted, the strip d', except at the ends, which are free, being sweated or otherwise secured to the face of the contact-bar d. The resistancesection c' having been placed upon the face of strip (l, the free ends ot' said strip are folded over, as seen in Fig. 5, to lie upon the top of the resistance-section, whereby the resistance-section is clamped in position by the clamping-strip d. When the several contact-bars and the resistance-sections mounted thereon are clamped in position between the casing-plates of the rheostat, the clampingstrip CZ is pressed into Iirm contact with the contiguous faces of the ribbon comprising the resistance-conductor.

I have shown in Fig. 5fL a modification in which the iiexible or free portions cl d are formed integral with the contact-bar.

As explained in my prior patent, above referred to, I preferably coat one face of the ribbon with an insulating material, so that when the same is formed into coils to constitute the resistance-sections the several turns or convolutions of the coils are relatively insulated.

The several contact-plates d d and the resistance-sections mounted thereon are adapted to occupy positions side by side, as illustrated, and to be clamped between the casing-plates, and the metallic casing-plates are insulated from the electrical conductors through theagency of the layers b b of insulating material. One end of the conductor cis wrapped about terminal plate e, to which is electrically connected the binding-post e', the binding-post e carrying a shank, which is electrically connected with said plate e and being insulated from the casing-plate a' by means of a block of insulation e2. The opposite end of the resistance-ribbon c is Wrapped about the terminal plate f, which is electrically connected with the bindingpost f', said binding-post being mounted upon the insulating-block f2. In order to firmly secure the terminal plates e and f in position and to electrically connect the ends of the ribbon c therewith, I provide a bridge-plate g, which is separated from the terminal plates by means of a sheet g of insulating material, as asbestos, this bridgeplate heilig clamped to the casing-plate by means of screws g2 g2. The end of terminal plate c constitutes one of the terminals with which the contact-arm of the rheostat is IOO ICS

ITO

adapted to engage, while the terminal plate f A is provided with an inwardly-projecting arm f2, to the end of which is secured a ring f3. The contact-spring h, adapted to be moved by the handle h', is arranged to engage at one end the projecting ends or terminals of the contact-bars,while the other end is adapted to make contact with the ring f3, connected with the terminal plate f. Current entering by binding-post f', for instance, may pass to ring f3, thence by contact-spring h to one ofthe terminals, and thence through the resistancesections in circuit to terminal plate e and to binding-post e. The spring-arm Zz is mounted 'upon a hub or casting h2, which in turn is mounted upon a rotating shaft h3, carrying. at the end the handle h2 A collar h4, carried upon the shaft h3, engages a bracket h5 to limit the lengthwise movement of the shaft h3. -The bracket h5 is secured byscrewshh6 to the clamping-plate a. A suitable bearingsleeve 71,7 is providedvfor the shaft h3,.this bearing sleeve beingv supported upon the bracket h5 and the casing-plate d. A tongue ffis formed from a portion of the terminal plate f to act as a stop or abutment to limit the movement of the contact-arm h. y

In order to more effectively secure the several parts of the rheostat between the casingplates a a', I formone or both, preferably both, of the casing-plates with a slight dish thereto-that is, slightly convex--so that when brought together the inner edges `of the annular plates will rest closer together than theouter edges.- edges toward each other the plates may be slightly-,sprung to therebyrmly clamp the contact-barsand resistance-sections in position. In assembling the rheostat I employ clamping-plates adapted to force the outer edges of the casing-plates toward each other and then' secure the outer edges of the casingplates together bymeans of a binding-strip 7c of sheet metal, oneedge of this strip of metal being folded upon itself to form a shoulder Za', adapted to rest against the outer face of plate d, while the other edge of said strip 7c is adapted to be folded over a ridge a2, bounding the plate a. The casing-plates are in this manner firmly secured together. This manner of securing the casing-plates together causes a firm -grip upon the contact-bars LZ, so as to prevent the same from being thrown out of their radial positions by the engagement of theicontact-arm h therewith. The movement of this contact-arm h is lateral with respect to the 'contact-bars, andif the sameare not firmly clamped in position there will be a tendency to shift these contact-bars laterally, thereby bringing the contact-bars into contact to short-circuit the resistancesections and otherwise render'- the operation ofthe rheostat unsatisfactory.

In order to insure the resting of the ends of the contact-bars in alinement and on a common level, I provide an insulating center plate Z, of porcelain or similar material. A series of holes m m are provided through the back casing-plate a, whereby suitable instruments may be inserted to temporarily support the center plate Z during the assembling of the rheostat and to force the face thereof upward under the ends of the contact-bars CZ cZ. Previous to this placing of the center plate in position the ends of the contact-bars d are bent to give to the same a tendency to extend downward rather than upward, and then as the center plate is forced upward against the ends of the contact-bars the ends By then forcing the outer thereof are all brought to a common level. Plaster-of-paris is then flowed into the spaces between the center plate Z and the back plate a and permitted to harden, whereby the cen- Y ter plate is securely fixed in position. The ring f3, connected with the terminal plate f, is adapted to rest upon the top of the center plate Z, and to accommodate the extending arm of the terminal platefa channel is formed in the upper face of the center plate Z.

Having described my invention, what I claim as new, and desire to secure by Letters Patent, is i 1. The combination with aresistance-ribbon of decreased width from one end to the other and formed into a plurality of resist# ance coils or sections arranged side by side, of contact-terminals electrically connected with said several sections and casings or yplates between which said several 'coil-sections are mounted and clamped, substantially as described.

2. The combination with a contact-bar, of a strip of flexible metal secured thereto and having the ends free and a coil formed from aribbon of resistance material resting upon said metallic strip, the rfree ends of said strip being folded over-.said coil, substantially as described.

3. -The combination with a plurality of contact-bars lying side by side, the endsof's'aid bars constituting the contact-terminals of a rheostat, of a flexible strip of metal secured vto the face of each of said bars, the ends of said strips being feee, and a resistance-ribbon formed into a plurality of resistance-coils one adapted to rest upon each of said flexible strips, the free ends of said strips being folded over the respective coils, substantially as described.

4. The combination witha contactbar and a coil formed from a ribbon of resistance material, ofa pair of free metallic portions in electrical contact with said contact-bar and adapted to fold over the ends of said coil, substantially as described.

5. The combination with a plurality of contact-bars resting side by side, the ends thereot' forming contact-terminals, of a plurality vof flexible metallic strips secured one to each IIO end wrapped around said terminal plate, and I a clamping-plate adapted to compress said ribbon against said terminal plate to eifect a firm electrical contact, substantially as described. A

7. The combination with the terminal plates e, f, of the resistance-ribbon having its opposite ends wound around the respective terminal plates, and the bridge-plate insulated from said terminal plates and adapted to compress the ends of said ribbon against said plate, substantially as described.

8. The combination with the contact-bars lying side by side and having the ends extended to form contact-terminals,of the center plate adapted to support said extended ends from beneath, substantially as described.

9. The combination with the'contact-bars occupying radial positions and having the inner ends extended to form contact-terminals, of the center plate having the periphery adapted to engage and support the ends of said contact-bars,substantially as described.

10. The combination with the casing-plates and the resistance-coils and associated parts clamped between the same, of the bindingstrip extending around the periphery of said casing-plates and serving to secure the same together, substantially as described.

1l. The combination with the casing-plates and the resistance-coils and associated parts clamped between the same, of the bindingstrip extending around the periphery of said casing-plates, and having the ends folded over to engage the edges of the casing-plates and clamp the saine together, substantially as described.

12. The combination with the casing-plates and the resistance-coils and associated parts clamped between the same, one of said casing-plates having a peripheral ridge extending around the same, of the binding-strip having one edge folded over to engage the edge of one of said casing-plates and having the other edge folded over the peripheral ridge on the other casing-plate, substantially as described.

13. The combination with the annular casing-plates formed so that the outer edges normally rest at a greater distance apart than the inner edges, of the resistance-coils and associated parts adapted to rest between said plates and the binding-strip for securing the peripheries of said plates in an approached position, substantially as described.

14. The combination with a plurality of resistancesections, and a series of contact-terminals connected respectively therewith, of a contact element adapted to sweep over said contact-terminals, said contact element and terminal being constructed so that the area of contact between the same diminishes step by step as the contact element is moved from one end of the series of terminals tothe other, substantially as described.

15. The combination with a pluralityT of resistance-sections, of a series of contact-bars connected respectively with said resistancesections and a contact element adapted to sweep over said contact-bars, said contactbars being ot' decreasing Width from one end of the series to the other, substantially as described.

16. The combination with a plurality of resistance-sections, of a series of contact-bars connected respectively therewith and arranged side by side,a contact element adapted to sweep over said contact-bars, the contactbars being of decreasing width from one end of the series tothe other and arranged so that as the contact element is moved to cut in resistance the same engages contact-bars of less width, substantially as described.

17. The combination with a series ot' contact-bars arranged side by side, the ends of said bars constituting the contact-terminals and being of decreasing Width from one end ot' the series to the other, of a resistance-ribbon formed into a plurality of resistancecoils, one of said coils being mounted upon each of said contact-bars, and a contact element adapted to engage the contact-termi nais, substantially as described.

18. The combination With the contact-bars lying side by side and having the ends extended to form contact-terminals, of an insulating-plate adapted to support said extended ends from beneath, substantially as described.

19. The combination with a series of' contact-bars arranged side by side, the ends of said bars constituting the contact-terminals, and being of decreased width from one end of the series to the other, of a resistance-rib bon of decreased width from one end to the other formed into a plurality of resistance coils or sections, the coils of greater width being mounted upon contact-terminals of greater width and vice versa, and a contact element adapted to engage the contact-terminals, substantially as described.

In witness whereof I have hereunto subscribed my narne in the presence of two wit- CHARLES WIRT.

Witnesses:

CHAs. L. 4LocKwooD, CHAs. M. LocKwooD. 

